A light emitting diode (LED) is a solid-state semiconductor element including at least a p-n junction. The p-n junction is formed between a p-type and an n-type semiconductor layers. When the p-n junction receives a suitable bias, the holes of the p-type semiconductor layer and the electrons of the n-type semiconductor layer are combined to emit light. Generally, the region emitting light is called a light-emitting region.
The characteristics of LEDs are small dimensions, high lighting efficiency, long lifetime, quick reaction, high reliability, and great chromaticity so LEDs have been applied widely in electronic devices, motor, signboard, traffic signals, and so on. With its full color spectrum, LEDs have been gradually replacing conventional lighting apparatus such as fluorescent lamps and incandescent lamps.
A liquid crystal display (LCD) has been utilized in variable kinds of electronic devices like the desktop computer or the laptop, the mobile phone, and the screens of the global positioning system (GPS) and the television. In general, the back light unit (BLU) provides a light source for LCD, and LED is one of the main light sources of the BLU. When the dimensions of the display tend toward smaller, the thinner thickness of the LED is preferred.